1. Field of the Invention
The present invention relates to a transformer having resonant inductance for zero voltage switching.
2. Description of the Related Art
Recent DC/DC power supply devices have the following two features.
First, they require a high input voltage. Recently, as the harmonic wave regulation tightens, a power factor correction circuit is universally and compulsorily used in various electric and electronic products. As a result, most power supply devices include a power factor correction circuit and a DC/DC converter. As for a general a power factor correction circuit, a booster converter is used. In the booster converter, an output is always higher than an input. Therefore, the output of the power factor correction circuit ranges from 385 to 415 Vdc on the basis of current common input line (85-265 Vac). As the output voltage is used as an input voltage of the DC/DC converter, most DC/DC power supply devices have a high input voltage.
Second, they required a low-voltage and high-current output. Processors which are driven at a low voltage are frequently used to reduce power consumption of communication devices. Further, for users' convenience, a number of functions are added to the respective processors, and thus power consumed in the respective processors inevitably increases. Therefore, most DC/DC power supply devices have a low voltage and high-current output.
As the DC/DC power supply devices have a high input voltage, a low output voltage, and a high-current output, voltage stress should be considered in the primary side, and current stress should be considered in the secondary side. Further, the DC/DC power supply devices should have a simple structure and a small volume, in order to implement high-power density. In general, as the switching frequency increases, the size of power devices decreases. In this case, however, efficiency decreases due to a switching loss. Therefore, zero voltage switching is essential for high efficiency. Further, the zero voltage switching is performed using leakage inductance and additional resonant inductance of a transformer.